Over the years there have been a number of possible sightings and a range of theories about what happened to the youngster, who would now be 26.

Earlier this year, South Yorkshire Police announced that they had received extra funding from the Home Office to help in the search.

Now, the official campaign to find Ben, headed by his mother, Kerry, confirmed that a team of officers will fly to Kos on Tuesday.

In a statement, Help Find Ben Needham said 10 officers were travelling to the island hoping to "find new witnesses as they urge islanders to come forward with any information which might help the case".

It said the officers will give a press conference at the farmhouse from where Ben went missing.

He had been taken to the site, in Irakles, by his grandmother, Christine Needham, to visit his grandfather, who was helping to renovate the run-down building.

Ms Needham said: "W e believe someone on Kos does know something - and if they do please come forward. It doesn't matter how insiginificant they think it is - if they have information let the police know."

In January last year, South Yorkshire Police and Crime Commissioner Alan Billings secured £700,000 of special funding from the Home Office to allow South Yorkshire Police to commit further resources to the investigation into Ben's disappearance.

This year, a further £450,000 was approved by the Home Secretary.

The Home Office backed a South Yorkshire Police operation in 2012 when land was excavated on Kos, near the farmhouse from where Ben went missing. No trace of the little boy was found.

In 2014, South Yorkshire Police asked the Home Office for the Special Grant Funding to follow up information the family believed had never been properly investigated.

In May last year, Ben's mother, sister and grandmother travelled to Greece with South Yorkshire Police detectives to make a direct appeal on a Greek television show about missing people.

Police have investigated a number of new lines of inquiry as a result of the programme and the ongoing investigation into the toddler's disappearance.

South Yorkshire Police confirmed the team will hold a press conference at the farmhouse on Tuesday.

A spokesman said the detectives will be "actively progressing lines of inquiry, distributing leaflets and posters, and carrying out house-to-house visits in Iraklis in Kos, where Ben was last seen".

Detective Inspector Jon Cousins said: "The lives of Ben Needham's family were ripped apart when he disappeared more than twenty years ago and their determination to find him has not diminished. They are more desperate than ever to find answers about what happened to him.

"It is likely that someone out there knows what happened to him and we will be appealing to people in Kos who have information to come forward and tell us what they know. The force is working closely with the Greek authorities to ensure a number of lines of existing inquiry are explored.

"We are also hoping that the offer of a Crimestoppers' reward of up to £10,000 could be an incentive for someone to finally come forward after all these years - it is not too late to tell us what happened and finally allow us to unearth the truth."

:: The Operation Ben team can be contacted on 0114 296 3022 or opben.needham@southyorks.pnn.police.uk.